This application proposes to establish and maintain a Coordinating Center to contribute to the overall Cooperative DATOS goals. This Coordinating Center will have three linked components: (a) coordinating cross-site activities; (b) conducting follow-up data collection, analysis, and reporting; and (c) working with NIDA Collaborating Scientists and Field Research Collaborative Center investigators. The Coordinating Center will have three specific aims: (1) Coordinate cross-site Cooperative DATOS activities to (a) facilitate collaborative analysis and reporting by performing executive secretariat functions, and (b) establish a repository for data and documentation from the DATOS family of studies and other databases, including TOPS, to encourage and support secondary data analysis for treatment and services research. (2) Conduct continuing follow-up studies of the 3,500 adult and 3,000 adolescent clients (and 1,500 parent/guardian collaterals of adolescents) interviewed in DATOS and DATOS-Adolescent in order to (a) provide longitudinal information on these treatment clients; (b) develop and test improvements in follow-up study data collection procedures, measurement, and analysis; and (c) investigate long-standing and emerging questions in substance abuse treatment and services research. (3) Work closely with NIDA Collaborating Scientists and Field Research Collaborative Center investigators in secondary analyses of methodological areas, overarching issues, and specific substantive research questions in DATOS and other databases. RTI will commit its resources and the unique qualifications of its staff to the Coordinating Center. The RTI team proposed to staff the Coordinating Center is committed to working collaboratively with the Cooperative DATOS teams and facilitate and implement the directives of the Steering Committee.